The goal of this project is an understanding of the molecular basis of the structure and function of inwardly rectifying potassium channels. These channels are central to the functioning of cardiac cells where they are involved in controlling the action potential waveform, duration, resting potential and controlling cell excitability. This proposal concentrates on the inward rectifier channels of the K1 class that show strong asymmetry in potassium conductance and are found prominently in heart and brain. The goal of this project is to use an integrated molecular, biophysical and biochemical approach to investigate a) the functional permeation, conduction and rectification properties of K1 channels, b) the channel polypeptide transmembrane topology, and c) the subunit composition and assembly of inward rectifier channels. The specific aims of the project are: Aim 1. The functional characteristics of the channels will be investigated to ascertain the molecular basis for channel pore properties, channel permeation and block, and channel rectification. Aim 2. The structure of the channel polypeptide across the cell membrane will be determined. Aim 3. The subunit composition of the channels will be elucidated, and the domains responsible for channel assembly will be ascertained. The results of these studies will provide new information about the molecular mechanisms involved in the function of the inward rectifier channels in the heart and brain. An understanding of the molecular architecture and function of the K1 channels will enable the development of K1 channel therapeutic agents to treat cardiovascular and neuronal disease.